In a cluster system in which a plurality of computers are connected, maintenance is performed upon these computers (hereinafter also referred to as nodes) without stopping the operations of the computers. Examples of maintenance performed upon a node include program updating. A software program implemented in a computer is updated as appropriate for various reasons. For example, in order to correct a bug (program error or program defect), extend the function of the computer, or fix a security hole (remove a weakness compromising the safety of a system), program updating is performed.
In the case of a certain type of program implemented in a system such as a cluster system in which a plurality of nodes operate in synchronization with each other, it is required that the versions (version numbers) of such programs be the same in all the nodes. If these programs are updated, it is required to update them at the same timing. Japanese Unexamined Patent Application Publication No. 10-334020 discloses a technique for transmitting information required for configuration change to all agents and then transmitting a configuration change start instruction to each of these agents. Using this technique, the configuration changes of the agents can be performed at the same timing.